Download What is a Mineral?

*What is a Mineral?*
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Naturally occurring
Inorganic
Solid
Definite crystalline structure
* = Most Important information
*Mineral characteristics*
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*Naturally formed
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*No substance created in a lab can be a
mineral.
examples: plastic, steel, sugar, paper
•
*Inorganic
– *Not living
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*Solid
– *Liquids and gases are not minerals.
examples: water, petroleum, lava, oxygen
*Mineral characteristics*
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Characteristic *crystalline structure
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*must have an ordered arrangement of atoms
*displays repetitive geometric patterns in 3-D
glass not a mineral (no internal crystalline structure)
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Definite *chemical composition
– *must have consistent chemical formula
examples: gold (Au), quartz (SiO2), orthoclase (KAlSi3O8)
basalt (like many other rocks) contains variable ratios of different minerals;
thus, has no consistent formula
Mineral Structure
Crystals: solids with atoms arranged
in orderly, repeating patterns.
*Some crystals form from magma, hot
melted rock below the Earth’s surface.
*When magma cools slowly, crystals
are large.
*When magma cools quickly, crystals
are small.
GRANITE ROCK
*Minerals
are the
building
blocks of
rocks
Mineral Structure
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*Contain one or more elements
which are made of atoms
*Most made of compounds of
several elements (Quartz SiO2)
Identifying Minerals
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*Six main properties:
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Color
Luster
Streak
Cleavage or Fracture
Hardness
Density/specific gravity
We will be testing these properties
in class during our mineral ID lab.
Identifying Minerals
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*Color:
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Most obvious, but often misleading
Many minerals have same/similar color
Different colors may result from impurities
Example:
Quartz
Identifying Minerals
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Luster:
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Metallic
example:
Galena
*How a mineral surface reflects light (shines)
Two major types:
 Metallic luster
 Non-metallic luster
Non-metallic
example:
Orthoclase
There are several terms used to
describe nonmetallic luster.
Examples could be vitreous,
like the quartz on the left, or
pearly, like the gypsum on the
right.
Other terms that might be used
include greasy, dull, and earthy.
Can you tell which of these has an
earthy luster and which has a
vitreous luster?
Vitreous
Earth
Identifying Minerals
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Streak:
*Streak – color of a mineral in powdered form
(used for metallic minerals)
Obtained by scratching a
mineral on a piece of unglazed
porcelain.
Example:
Hematite
The streak is often not the
same color as the mineral.
A minerals color may vary, but
the streak rarely will!
*Identifying Minerals*
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Cleavage vs. Fracture:
*The way a mineral breaks
– Cleavage: tendency of a mineral to break
along planes of weakness (smooth)
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– Minerals that do not exhibit cleavage are said
to fracture (uneven)
*Minerals with cleavage break along
smooth, flat surfaces.
Physical Properties of Minerals
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*Fracture:
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minerals that do not exhibit cleavage are said to
fracture
*minerals with fracture break with uneven,
rough, or jagged surfaces
Identifying Minerals
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Hardness:
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*How easy it is to scratch a mineral
Mohs Scale of Hardness
 relative scale
 consists of 10 minerals, ranked 1 (softest)
to 10 (hardest)
Mohs Scale of Hardness
Hardest (10) – Diamond
Softest (1) – Talc
Common objects:
- Fingernail (2.5)
- Copper penny (3.5)
- Wire nail (4.5)
- Glass (5.5)
- Streak plate (6.5)
Identifying Minerals
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Specific gravity:
*weight of a mineral divided by weight of an
equal volume of water
 metallic minerals tend to have higher specific
gravity than non-metallic minerals
Galena
SG=7.5
Quartz
SG=2.67
Specific Gravity/Density
=
*Density – how much matter is in
something (Density=mass/volume)